In my prior U.S. Pat. No. 4,097,134, and in other prior art cited in my copending application, various methods and apparatus for displaying map information are proposed. This prior art is relatively complex and expensive. In general, the prior art may use a fixed magnification with a continuous map image of one scale, at times in conjunction with a parallel image strip illustrating places of interest along the route. In other instances, the displaying optical system may be of variable magnification to allow zooming in on a particular area of interest on the route being displayed. One of the difficulties attendant upon variable magnification, aside from the complexity and expense of the optical system, is the fact that any lettering or indicia used for identification purposes will be usable only at low magnification and at high magnification will tend to obscure or obliterate the enlarged image, or at lower magnifications, will be too small to be intelligible.
Accordingly, it is an object of the invention to provide a map projection system which addresses the problems extant in the prior art.
In one aspect, the invention concerns the method of displaying map information which comprises the steps of providing at least two map images of the same terrain but of different scales from each other; selecting a portion of one of the map images and displaying such selected portion at fixed magnification to permit examination of the display with the detail determined by the scale of the one map image and the fixed magnification; and then displaying, at the fixed magnification, a portion of the other of the map images which corresponds with an area of the selected portion of the one of the map images to examine the display of the other map image in that detail permitted by the scale of the other of the map images at the fixed magnification.
In another aspect, the invention concerns the method of displaying map information which comprises the steps of providing at least two map images of the same terrain but of different scales from each other; displaying a selected portion of one of the map images at fixed magnification; and switching the display from the selected portion of the one of the map images to a corresponding selected portion, at the same fixed magnification, of the other of the map images. In this way, a simple, compact and relatively inexpensive optical system of fixed magnification is employed at all times while the viewer is permitted to switch from a display of a particular portion of one map image to a display of a corresponding portion of another map image of a different scale. In this way, a display of a portion of a small scale map image will reveal a large area of small detail and by switching to the corresponding portion of a larger scale map image, greater detail will be revealed. As used herein, "corresponding portion" is meant to refer to corresponding portions of two (or more) map images of different scales in the sense that the central point of each such portion will be the same. That is, it will be appreciated that although the display area does not change in size, when switching from a display of one map image scale to another, the relative area of map image being displayed will change. However, the system is such that the center point of the display of any scale map image will always be centered when switching takes place so that if the viewer switches while the center point of the displayed map image is on or about on the region in which he is most interested, the display when switched will still be centered on the same center point and the new display will encompass the desired region irrespective of the scale to which switched.
In accord with an object of the invention, it is of importance that the magnification remain fixed in order to simplify the optical system utilized and to avoid the use of movable parts or components which could introduce distracting and unacceptable movement of the displayed information. This is particularly important if the system is to be employed in, for example, automobiles or the like.
The invention is also concerned to provide an apparatus which comprises the combination of at least two map images of the same terrian but of different scales from each other; means for displaying a selected portion of one of the map images at fixed magnification to permit examination of the display with the detail determined by the scale of the one map image and the fixed magnification, and for also displaying, at the fixed magnification, a portion of the other of the map images which corresponds with the selected portion of the one of the map images to permit examination of the display of the other map image in that detail determined by the scale of the other of the map images at the fixed magnification.
Apparatus of this invention also concerns a support having images of at least two maps having different scales and depicting the same terrain areas, the map image of smaller scale being of small size compared with the size of the other map image of larger scale, means for displaying a portion of a selected one of the map images at a fixed magnification, and means for switching the fixed magnification display from the portion of the selected one of the map images to a corresponding portion of the other map image.
It will be further appreciated that the system according to this invention requires that the composite of the map images, whether there be two or more separate images, be accurately oriented between or among the separate images of different scales. This accuracy is necessary in order to simplify the arithmetic operations involved in switching from one map image to another. For example, a particular point on a map image having one scale is easily defined in terms of its orthogonal coordinates but also requires a knowledge of the various map image scales involved if a switch to the same particular point on a map image of different scale is to be effected. Further, simplification is maintained if the relative displacements between the optical system and the map image composite are effected in consonance with the orthogonal coordinates. Still further, simplification is maintained if the shapes of each separate map image of the composite are rectangular, with the edges or borders of each map image extending in the coordinate directions. Another consideration of a practical nature concerns elimination of dual display or partially blank display which could occur under certain circumstances. For example, if two map images are closely adjacent or in touching relation, parts of both map images could be displayed at the same time, or if the edge or border of a map image is overlapped in the display and no other map image is adjacent, the display will be partially blank where the display extends beyond the border. Elimination of these phenomena may be effected by limiting relative movement between the optical system and the map image composite so that the center point of a square display may not approach the border by a distance less than one half the width of the field of view of the display.
Another object of the invention is to provide a microfiche representation of spatially separate first and second map images of the same terrain and having different scales so as to be examined individually at fixed magnification to reveal details of corresponding portions of the map images permitted by the individual scales of the two map images and the fixed magnification.
These and other objects of the invention will become more apparent as this description proceeds.